rank: used when organs such as leaves are arranged in vertical series (distichous = two-ranked, etc.); also used to refer to the degree of branching.

rank: in the taxonomic hierarchy, one of the levels assigned to plant groups; these denote relative inclusion relationships, e.g. a family will include a genus or genera, but not vice versa; members of the one rank are not equivalent other than - one hopes - all being monophyletic and are therefore not really comparable; for the main ranks mentioned here, seeclass, order, family, genus, species (which may well not be monophyletic...).

recalcitrant: of germination, and sometimes also pollen viability, the seed or pollrn grain needing to remain hydrated if germination is to occur and not tolerating drying or freezing (and often even temperatures below 100 C), c.f.orthodox, see alsoafter-ripening.

receptacle: the axis of a flower on which the perianth, androecium and gynoecium are borne; in Asteraceae, used to refer to the often swollen and apically flattened part of the stem bearing the flowers and inflorescence bracts; in monilophytes, the part of the sorus bearing sporangia.

receptacular epigyny: of epigyny, when the floral apex is initially convex, but after gynoecial initiation the periphery of the floral apex expands and raises, forming a basin in the center of which the carpels are borne and on the periphery of which the perianth members and androecium are borne, i.e. epigyny is due to development of axial tissues (Kuzoff et al. 2001), c.f.appendicular epigyny.

reiteration: of plant architecture, when the characteristic construction of the individual is repeated by branch systems that develop on a plant after damage, or sometimes as the result of natural causes.

resupinate: of floral symmetry, twisted through 180o, e.g. as with
the ovary of many Orchidaceae; note that resupination may result in the flower maintaining an inverted (as in Orchidaceae) or "normal" position (as in Thunbergia mysorensis - see Bell & Bryan 2008).

reticulate: in leaf venation, where the veins join or anastomose (so technically forming cycles), one of three terms that describe the basic organization of venation, see alsodendritic and hierarchical; in addition, a rather loose term describing leaves where reticulation and anastomosis predominate in the venation, c.f.parallel-veined.

rhipidium: of a monochasial cymose inflorescence of some monocots,
flowers arising successively from the adaxial prophylls, thus alternating from one side of the axis to the other side, and all being in a single plane, the whole inflorescence often appearing corymbose from a lateral view, c.f.drepanium, helicoid cyme, scorpioid cyme.

rhizoid: unicellular trichomes on the collar in seedlings, especially those of monocots; basically precocious roothairs, but longer, denser, and/or living longer, but of course also different in position.

rhizosheath: made up of mucilage from the root cap, root cap cells (maybe living), soil particles, bacteria, etc., all anchored to root hairs and forming a sheath surrounding the young root; found e.g. in many Poaceae (McCulley 1995), c.f.dauciform root clusters, also rhizosphere.

rhizosphere: the soil immediately surounding the root, influenced by secretions from the root and bacteria associated with the root, c.f.rhizosheath.

rootstock: a short, erect, more or less swollen structure at the junction
of the root and shoot systems of a plant, c.f.xylopodium.

rosette leaves: the leaves at the base of the stem when these are separated by very short internodes and lie more or less flat on the ground, so forming a circle, see also basal and radical leaves, c.f.cauline.

rotational: on of the basic types of symmetry, identity of two figures after rotation of the first, thus the flowers of Vinca show a 5-fold rotational symmetry achieved after bringing the five asymmetrical corolla lobes sequentially to the upper (or other invariant) position, c.f.reflectional and translational.

scorpioid cyme: a monochasial cymose inflorescence
branching alternately from a bracteole/prophyll on one side of a pedicel and then from one on the other side, the flowers being borne in two rows, the whole more or less zig-zag but also coiled like the tail of a scorpion, c.f.drepanium, helicoid cyme, rhipidium, see alsoacervulus. (bottom left hand image).

semidry: of the surface of the stigma, which has secretory cells, but the exudate is retained by the cuticle and/or protein pellicle, but these can be ruptured by pressure exerted by the exudate or by physical friction (Verstraete et al. 2014), as by the pollinator, c.f.dry, and wet.

senescence: age-related processes that signal the beginning of the death of a plant or plant part.

sensu lato: after a name, meaning that the name is to be taken with a broad circumscription, often s. lat., c.f.sensu stricto.

sensu stricto: after a name, meaning that the name is to be taken with a narrow circumscription, often s. str., c.f.sensu lato.

sepal: a member of the (usually green) outer whorl of non-fertile
parts surrounding the fertile organs of a flower, c.f.epicalyx,
petal, tepal.

sepaloid: looking like sepals, e.g. of bracts,
when green and arranged in a ring beneath a flower.

septal nectary: a nectary consisting of a more or less complexly organised epithelial surface in the septum or septal radius of the ovary in angiosperms, so far known only from monocots in which carpels are initially free, intercarpellary fusion being postgenital.

serial homology: similarity between two structures in the one organism because of their common origin as some kind of repeated structure, i.e. the legs on successive segments of a centipede or leaves occuring on different parts of the plant, c.f.analogy, homology, homocracy, homoeology, paralogy.

seriate: in rows or whorls, often used as a suffix, as in 2-seriate, biseriate, etc.

shoot apical meristem (SAM): a group of pluripotent cells at the apex of a stem from which stems, leaves and reproductive structures differentiate, seecorpus, tunica (a histological zonation in angiosperms and Gnetales).

shoot unit: the structure that develops from a single shoot meristem, whether initially apical or axillary, as in the individual sympodial units.

short-day: of a photoperiodic response, where short periods of light alternating with long periods of dark are neeeded for flowering to occur (more accurately, a long uninterrupted period of dark), c.f.long-day.

short shoot: a shoot in which the internodes elongate little or at all, bearing reproductive structures and/or leaves, when well developed, as in Ginkgo and some apples, rather spur-like, c.f.long shoot, the comparison often being made between axillary shoots; see also proliferation.

sieve cell: a conducting cell in phloem tissue of gymnosperms, elongated, nucleate, and not necessarily derived from the same mother cell that produces the closely associated Strasburger cell, the sieve areas being relatively unspecialised and the pores apparently filled with membranes that are continuous with smooth endoplasmic reticulum in the adjacent cytoplasm, there also being a central cavity in the area of the middle lamella, c.f.sieve element and sieve plate.

spathella: as in some Podostemaceae, a small, closed membranous
sac which envelopes the immature flower, rupturing irregularly as the pedicel
elongates at anthesis.

spathulate (= spatulate): spoon-shaped; broad at
the tip and narrowed towards the base.

species: a taxon comprising one or more populations of individuals
capable of interbreeding to produce fertile offspring and not so interbreeding with other species, or a group of organisms phenetically distinguishable from other such groups, or...., the lowest major rank of the taxonomic hierarchy, c.f.class, family, genus, order.

spikelet: part of the inflorescence, especially in grasses, sedges and
some other monocotyledons, a racemose unit consisting of one or a few closely-packed florets born along a rachilla and subtended by two
glumes, etc.

spine: a stiff, vascularised, sharp-pointed structure, formed from a leaf or part of a leaf such as a stipule, leaf tooth, etc., c.f.prickle, thorn.

sporopollenin: the most highly decay- and chemical-resistant biopolymer known, made up of cross-linked phenolics and hydrocarbons that covers pollen grains in particular and embryophyte spores in general (but not the megaspore in flowering plants).

staminal corona: in Apocynaceae-Asclepiadoideae,
fleshy outgrowths of tissue, attached abaxially to the staminal column at
the bases of the filaments or on the backs of the anthers, see gynostegial
corona.

stegmata: SiO2-containing cells usu. adjacent to vascular tissue, the wall adjacent to the underlying sclerenchyma thick, the anticlinal walls thinner, and the outer periclinal wall thinnest; the term rarely used when the cells are epidermal.

stem-based: a way of defining a clade in which the basal part of an internode on a cladogram is the defining point, e.g. the clade consisting of A and all organisms that share a more recent common ancestor with A than with B, c.f.apomorphy-based, node-based.

stem group: that part of a clade between the common ancestor of the clade as a whole and the common ancestor of the extant members of the group, c.f.crown group.

stemonozone: zone in which petals are adnate to a tube formed by connate filaments, as in some Fabaceae (see McMahon & Hufford 2002), essentially an epiandroecial corolla, c.f.hypanthium, stapetalum.

steroids: a large class of organic compounds characterized by a nucleus of 17 carbon atoms in the form of four fused rings (three containing six carbon atoms and one containing five), derived from triterpenes, and with varying substituents and degrees of unsaturation, including sterols, cardiac-active glycones, bufadienolides, cardenolides, and some sapogenins and alkaloids; seephytoecdysteroids..

sterols: terpenoids, solid, unsaturated steroid alcohols with an -OH group at the C3 position (bottom left below) that occur both free and as esters or glycosides, and are classified according to the organism in which they are found as mycosterols, phytosterols, etc.

stomatal index: the proportion of stomata to other epidermal cells - (S/E + S) x 100, where S is the number of stomata and E the number of epidermal cells in a particular area of leaf blade.

stomium: the region of a sporangium in/down/along which dehiscence occurs, e.g. of an anther in
flowering plants; it includes structural attributes that change over the course of anther ontogeny to give rise to the dehiscence region (see Hufford & Endress 1989, p. 303), pl. stomia.

Strasburger cell: a nucleated cell in phloem tissue of gymnosperms that is closely associated with a sieve cell; the metabolisms of the two are intimately connected such that one cell will die soon after the other, but the albuminous cell is not necessarily derived from the same mother cell that produces the sieve cell, c.f.companion cell.

suspensor: a part of the proembryo and derived from the basal cell of the two-celled embryo, often a single file of cells developing at the micropylar end and terminated by the basal cell, not contributing to the embryo proper, probably equivalent to the foot of lycophytes, etc. (Johnson & Renzaglia 2009), c.f.hypophysis.

suture: a line of junction between two fused organs, sometimes also a line of
dehiscence.

sympodial: of growth, without
a single, persistent growing point, the apical meristems aborting or being converted into flowers and growth being continued by axillary buds that successively replacing the terminal buds, of a stem,
growing in the above manner, see alsocymose, determinate, c.f.monopodial.

syndrome: a distinctive combination of features, often used in the context of fruit dispersal and flower pollination, whether or not (the latter is usual) any one of those features is unique to or even constant in a particular syndrome.

tannins: complex, aromatic compounds (phenolics) that precipitate proteins occurring especially in the bark of
many shrubs and trees, varying considerably in chemical composition and with different biosynthetic pathways and so a term of little use, see ratherproanthocyanidins, hydrolyzable tannins; tanniniferous, producing tannins.

tendency: a rather vague and historically fraught term one meaning of which refers to features that have evolved separately, but are similar enough to pass Remane's criteria of similarity ("homology"), because of common ancestry, = parallelism. Another less precise meaning, is sometimes or almost - "such-and-such a group has a tendency to be a tree".

tendril: a slender climbing organ formed by modification of a stem, a leaf or leaflet; G fibres are involved in their activity (Bowling & Vaughn 2009).

thalamus = receptacle (as in the old Thalamiflorae), but there are other meanings, too; the term should certainly be discarded (Rickett 1954b).

thallus: a more or less flattened vegetative body of a plant that is not differentiated
into organs such as stems and leaves, e.g. the gametophytes of many hepatics and all hornworts (c.f.protonema), the plant body of flowering plants such as podostems
and Araceae-Lemnoideae.

thermogenesis: respiratory heat production, whether by the mediation of alternative oxidases (catabolizing lipids) or by uncoupling proteins (carbohydrates) in some variants of entomophilous pollination.

tiglic acid: a hemiterpenoid (C5 H8), trans-2-methyl-2-butenoic acid, an unsaturated fatty acid with an isoprene skeleton, posssibly not biogenetically related to the terpenoids, more probably derived from leucine.

Tiglic acid, C5 H8 O2.

tile cells: radial files of dead, empty, erect cells in vascular rays, much narrower radially than the procumbent cells of the ray and interspersed among them, seeDurio and Pterospermum types.

tilosomes: often distinctively branched masses of cellulosic and/or ligneous material coming from the inner periclinal wall in the innermost cells of the velamen adjacent to the passage cells in the exodermis, esp. in Orchidaceae.

tissue: a part of a plant made up of one or more cell types and usually with one or a few functions, c.f. alsoorgan.

tocopherols: a class of various methylated phenols a number of which have vitamin E activity, tocotrienols, which may show similar activity, have three double bonds in the side tail.

tolypophagy: a condition common in orchidaceous endomycorrhizae where fungi penetrate cells via pit fields and pelotons are formed in the cell, then they may be lysed, but there is no lysis of orchid tissue (see Rasmussen & Rasmussen 2014), c.f.ptyophagy.

translational: on of the basic types of symmetry, of something like a frieze that can be divided by straight lines - horizontal, vertical, etc. - into a sequence of identical figures, c.f.reflectional and rotational.

transseptal bundle: in floral anatomy, the vascular bundles to the ovules in a fully syncarpous gynoecium that do not run up the ovary in the axial tissue, but they are found in the ovary wall, curving over at the apex and finally supplying the ovules,
c.f.dorsal bundle, ventral bundle.

trilete: the triradiate or Y-shaped scars on the proximal poles of pollen (actually, prepollen) representing the points of junction of the pollen tetrads, they are weakened areas involved in germination, not occuring in angiosperms, c.f.monolete.

tristylous: a variant of heterostyly in which there are flowers of three different kinds in the one species, in each plant all flowers have styles of only one of the three possible lengths
(short, mid, long), the stamens being in two whorls of the two complimentary lengths, c.f.distylous.

utricle: a small bladder; a small, bladdery, more or less inflated, dry, single-seeded fruit, a variant of achene s.l., sometimes the fruit itself is surrounded by an appendicular structure, seeperigynium s. str., c.f.caryopsis, cypsela, nut.

vegetative reproduction: a rather confusing term, sometimes referring to reproduction that does not involve the production of seeds (as used here), sometimes to all reproduction that does not involve normal meiosis and fertilisation, i.e. apomixis s.l., c.f.amphimixis.

velamen: an often distinctively-thickened water-retaining outer part of the aerial roots of
some epiphytic and epilithic plants, especially monocots, consists of one to several layers of dead cells, derived from the rhizodermis, bordered (?always) internally by the exodermis, seetilosomes.

ventral: of a lateral organ, of the side
towards the subtending axis in early development, so it is sometimes used to refer rather counter-intuitively to the upper surface of a leaf blade, however, the term is also used in the opposite sense, so it is very confusing, = adaxial,
c.f.dorsal.

ventral bundle: in floral anatomy, the vascular bundle running up the middle of the carpel wall, between the septae and not asssociated with the placentae, "the midrib bundle of the carpellary leaf",
c.f.dorsal bundle, transseptal bundle.

ventricidal: in fruit dehiscence, when the opening is along the inner or ventral (= adaxial) side of a carpel; this is a curious term, since if applied to a fruit made up of a single carpel, then it is equivalent to a
c.f.follicle, so it can really be applied only to a syncarpous fruit, and in such cases where individual carpels have separated septicidally they are then described as opening adaxially.

vessel: a capillary tube formed from a series of dead cells, the vessel elements,
in the xylem, the end walls having broken down all or in part and forming scalariform or simple perforation plates, seetylose, c.f.tracheid.

vestured: of pits, bordered in particular, the wall facing the lumen more or less lined with small wart-like protuberances or projections (the vestures) that are branched or not, c.f. alsoscalariform, simple.

viscous: of a liquid, not pouring freely, having the consistency
of syrup or honey.

vittae: oil-containing sacs or tubes, as in the fruits of many Apiaceae, sing. vitta; OR, caulescent species of Vallisneria (Hydrocharitaceae).

viviparous: of seeds, germinating and the seedling becoming apparent before being
shed from the parent plant (see Rhizophora, etc.), often also extended to include plants that produce plantlets from vegetative meristems in the inflorescence (= pseudovivipary), c.f. cryptovivipary.

water gap: a small specialized anatomical structure in the pericarp or seed coat allowing water to enter physically dormant seeds and allowing the process of germination to begin (Turner et al. 2009), c.f.operculum.

wing: a flattened expansion of a fruit, seed or pollen grain;
a thin flange of tissue extended beyond the normal outline of a stem or
petiole; relatively large lateral spreading structures, whether petals or sepals, in a papilionoid flower, c.f.keel, standard.

withanolides: steroidal lactones characterised by ergostane type steroids with a C28 basic skeleton having a side chain of C9 units of which a six-membered lactone ring is a characteristic feature.

xeromorphic: referring to the structural
features usually associated with plants of arid habitats (such as hard
or succulent leaves), although the plant is not necessarily drought-tolerant, seeericoid leaf, sclerophyll, c.f.scleromorphic.